rr i 96 RATIONAL CONSTRUCTION OF FURNACES It is comparatively easy to correct these regenerators in a manner which will cause them to work better. Fig. 55 shows the correction or change which should be made. [This change, however, does not affect the frictional resist- ance of this type of checker work.] The hot gases enter the top part of the cham- ber and leave at the bot- FIG. 56. torn; the height of the cham- ber h may be calculated according to the formula of Professor Yesmann in the same manner as the height of the flues leading to the reversing valves; in this way it is possible to design these chambers of such a height that the lower free surface of the current of gases will be at the level of the bottom of the chamber. The checkers designed by Dalen (a well-known German designer of fur- naces) show a construction equally erroneous (Figs. 56 and 57). Here the hot gases are conducted into the checker cham- ber, not at the top, but below the middle of the chamber. Such a regenerator heats the gas nicely (Fig. 56), but it works very in- efficiently, because the heated gases are very light and the hottest gases are trapped in the upper part of the cham- ber and cannot pass out to the flues, while the upper portion of the checker does not do any work at all and forms a pocket filled with immobile heated gas. Fig. 58 shows a horizontal regenerator constructed in a rational FIG. 57. FIG. 58.